Frames and scrolling problem

I'm trying to put the grid in the top of a resizable frameset of 2 rows on top of each other. For example:

<frameset  rows="50%,*">
    <frame name="gridFrame" src="grid.html" marginwidth="0" marginheight="0" scrolling="true" frameborder="1">
    <frame name="details" src="details.html" marginwidth="10" marginheight="10" scrolling="auto" frameborder="1">
</frameset>

Resizing or not, the scrollbar that appears has the bottom part of the scrollbar hidden by the frameborder, so I can't scroll to the bottom of the grid and see its contents. This happens in both 1.0.3 Firefox and 6.0.2900 IE. I'm on XP SP2 if that matters.

Any help on getting this to show up correctly?